WEDNESDAY, Sept. 12 (HealthDay News) -- Stress causes the bodies of some black people to retain as much salt as eating an order of french fries, which boosts their blood pressure and increases their risk for cardiovascular disease, a new study finds.

The U.S. researchers found that when stressed, about 30 percent of blacks are salt retainers. In response to stress their body holds on to about 160 milligrams of salt and their systolic blood pressure (top number in a blood pressure reading) goes up about seven points above normal and stays elevated for about an hour.

Over the course of a day, this stress response adds a daily sodium load of about 500 milligrams to a typically salt-heavy diet, according to study author Dr. Gregory Harshfield, a hypertension researcher at Georgia Health Sciences University, in Augusta.

The Institute of Medicine, a nonprofit American organization that dispenses health advice, recommends a daily sodium intake of less than 2,300 milligrams, preferably less than 1,500 milligrams. Average daily salt consumption in the United States is about 3,700 milligrams, the researchers said in a university news release.

"Everybody knows stress is bad for you and everybody has the perception that a high-salt diet is bad for you, and both are particularly bad for these individuals," Harshfield said in a university news release. "Every time they are stressed, they hold onto as much salt as you get eating a small order of french fries and this can occur many times over the course of even a good day."

This increased retention of sodium likely causes blood pressure to stay elevated even during sleep, which should be a recuperative time for the body, Harshfield noted.

The study was scheduled for presentation Sept. 7 at the Psychogenic Cardiovascular Disease Conference in Italy.

Harshfield has shown that this dangerous sodium load can be reduced with widely used high blood pressure drugs called angiotensin receptor blockers, according to the release. However, these drugs are rarely used in blacks because they tend not to have high levels of the blood vessel constrictor angiotensin.

Blacks with this type of stress response would likely benefit from a low-salt diet as well, Harshfield said.

Data and conclusions presented at medical meetings should be considered preliminary until published in a peer-reviewed, medical journal.